Semiconductor micro-circuitry is formed on substrates using a widely varied number of fabrication processes. One part of such fabrication processes frequently includes the photolithographic patterning of surfaces to generate the desired structural patterns on a semiconductor substrate surface. As is known to those having ordinary skill in the art such photolithographic patterning generally involves image transfer from a mask pattern onto the substrate surface.
Commonly, this means that layer of material known as photoresist is coated onto the top layers of a substrate. Both positive and negative photo resists are used as process circumstances are required. A mask pattern is then commonly used to controllably expose various parts of the photoresist to an exposing light beam. The photoresist is developed to reveal a desired transfer pattern in photoresist. Subsequent processing can be used to etch away the exposed surfaces of the substrate to achieve a transfer of the pattern into the substrate.
After patterning the photoresist is removed. Commonly, the photo resist is removed in a process chamber referred to as a strip module. Typically, a photoresist stripping process takes about 5 minutes. This presents a significant processing bottleneck as such stripping takes significantly longer than most of the other associated process steps. Once tools for stripping photoresist become fouled by process detritus, their stripping efficiencies can deteriorate rapidly. In some cases the deterioration is so marked as to double (or more) the stripping process times. This makes an existing process bottleneck significantly worse. The present invention is intended to address some aspects of this problem.
FIG. 1 schematically depicts a simplified schematic view of an ordinary photoresist stripping tool and is accompanied by the following brief description of its operation. One example of such a tool is a Conductor Etch 2300 MWS strip module produced by Lam Research Corporation of Fremont, Calif. The schematically depicted tool is shown in cross-section view. An example strip chamber 100 includes a pedestal 102 that holds the substrate 104 (commonly, a semiconductor wafer) having photoresist material formed thereon. The microwave strip chemistry applicator assembly 101 is positioned in the chamber 100. The applicator assembly 101 typically comprises an application tube 103 positioned inside a RF coil 106. Strip gasses 105 are flowed into the application tube 103. In one typical application, the strip gases can include, O2, N2, H2O, CF4, or other suitable materials. As the gasses are flowed through the application tube 103 the coil 106 is energized. The electric field created by the coil is sufficient to ionize the strip gases. The ionized strip gases pass out of the tube 103 as effluent plasma 106e which strips the photoresist from the substrate 104.
Over time, the effluent and the residue generated by the stripped photoresist coat the chamber walls and deposit on the inside of the walls of the tube 103. The unfortunate effect of this process is that the accumulated residue changes the strip rate of the stripping process. As an unfortunate consequence, the strip times can be doubled or more in a matter of months due to the accumulation of undesirable residues on the inner tube walls. Previously, the solutions have been to supply a new application tube once the process degradation has become too great. This is an expensive solution and can take the strip chamber out of commission while a new tube is being shipped and installed. Thus, it would be preferable to develop suitable cleaning process that would enable the application tube to be returned to use in relatively short order without the need to replace the tube every three months.
For these and other reasons, an effective microwave applicator tube cleaning process is needed.